Hi Katie
The exercise ring on Apple Watch (part of the Activity app) requires activity above a "brisk walk" - with a sustained increase in heart rate for at least 1 minute - in order to give credit.
If you are not using the Workout app, it's important for your arm to swing naturally as you walk or run, because the Activity app relies on arm motion and the accelerometer to track movement.
Also, to get the best results from the Activity app, ensure that you have Wrist Detection turned on (Apple Watch iPhone app > General > Wrist Detection toggle).
You can certainly record brisk walks as workouts: use the Workout app (eg Outdoor Walk activity) and start and end your activity accordingly.
If you also take your iPhone along on outdoor walks (with the appropriate settings selected - see below), you can calibrate your Apple Watch. This will enable it to more accurately recognise and record activity, including for the Activity app.
During Workouts, ensure that Apple Watch is fitted snugly to your wrist so that the sensor can measure your heart rate (which happens continuously during workouts).
More info:
Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support
Use the Activity app on your Apple Watch - Apple Support
Use the Workout app on Apple Watch - Apple Support
